1. Field of the Invention
The present invention relates to a method for managing a light exposure mask (hereinafter, also referred to as “mask”) which is used in a lithographic step of a semiconductor manufacturing process, and to a light exposure mask.
2. Description of the Related Art
As the fine structure and high integration of a LSI pattern progress in recent years, in a lithographic technology for use in pattern formation, a shorter wavelength is being used. For example, a light source of a light exposing apparatus such as g-ray (436 nm) and i-ray (365 nm) of a high pressure mercury arc lamp was conventionally used, but now, KrF excimer laser (248 nm) and ArF excimer laser (193 nm) are used. Because such an exposure light source emits light with a short wavelength and has a high output, the energy of the emitted light is high. Thus, this causes a phenomenon that a foreign matter, which grows with the elapse of time, occurs on a mask used for light exposure so that the mask is contaminated. It is reported that this growing foreign matter (which is also referred to “Haze” or “clouding”) occurs remarkably as the wavelength of an exposure light is shorter. When the growing foreign matter occurs on the mask get larger to such an extent that the foreign matter is transferred to a wafer, it causes break or short circuit in a circuit of a semiconductor device.
As one of the major factors of occurrence of the foreign matter, which contaminates the light exposure mask when the light source with a short wavelength exposure light is used, it is reported as follows. A sulfate ion, which is an acidic substance used for mask washing and remains on a mask surface after mask manufacturing, and a basic substance such as ammonia, which is present under a mask usage environment, are reacted by irradiation with an excimer laser during pattern transfer so that ammonium sulfate or the like occurs as a foreign matter (for example, see Japanese Patent Application Laid-Open (JP-A) Nos. 2006-11048 and 2004-53817).
For this reason, there is a problem that, although a mask has a good quality with no defect in inspection after mask manufacturing, a foreign matter occurs on the mask to contaminate the mask during repetition of excimer laser irradiation in a light exposure apparatus. Whereby, a good pattern transfer image cannot be obtained on a wafer. In particular, there is a problem that a foreign matter, occurs on a transparent region or a semi-transparent region on the mask, changes the transmittance of exposure light. In some cases, although a mask is in a good state at the beginning of use, a foreign matter may grow as a contaminant with the elapse of time. Further, a foreign matter may occur on a certain mask even when the light exposure amount is small. These cases are difficult problems in management of a mask.
Regarding the above-mentioned problems of the growing foreign matter which contaminates a mask, as a method for managing a light exposure mask, there are proposed, for example: a method of rewashing a mask at every time when an accumulated light exposure amount (accumulated irradiation amount) becomes a predetermined value; a method of rewashing a mask in a case of observing a foreign matter in inspection of the mask at every predetermined value of an accumulated irradiation amount; a method of providing a foreign matter evaluation portion on a mask and evaluating a usage limit of the mask (for example, see JP-A-2005-308896); and a method of rewashing a mask in a case of observing a defect common to chips on a wafer surface, in inspection of every predetermined lots of light-exposed wafers.
However, the above-described managing method using an accumulated irradiation amount has its disadvantage as follows. Although masks have the same quality regarding a remaining component on a substrate, the occurrence frequency of a foreign matter is different among the masks depending on the usage environment of the mask and the like. Therefore in some cases, failure occurs on a wafer before the accumulated irradiation amount becomes a predetermined value. When the frequency of mask washing is increased in order to prevent such a failure from occurring, there is a problem of increasing manufacturing time and cost. The managing method of combining the accumulated irradiation amount with mask inspection has a problem that even though the failure is prevented from occurring, the inspection is weighted to cause increased costs depending on increase in inspection time. The managing method of providing a growing foreign matter evaluation portion on a mask is a restrictive method only used for a specific mask and has no general versatility. The managing method of inspecting a wafer includes a destructive inspection, and therefore there is a problem of causing a plurality of wafer chip defect failures.